1. Field of the Invention
The present invention relates to a method and an apparatus for performing recording by heating and driving recording elements.
Recording apparatuses benefitting from this invention can be used in a facsimile machine, a typewriter, a copying machine, and a printer. Recording systems for performing recording upon heating of heating elements which can employ the present invention include so-called ink-jet, thermal transfer, thermal, and electrothermosensitive recording systems.
2. Related Background Art
Related arts will be described by exemplifying a thermal printer as a recording apparatus.
When a conventional thermal printer is operated at a low ambient temperature or a time interval to the next recording cycle is prolonged, a thermal head is undesirably cooled. Even if the thermal head is energized within the same period of time as in the previous recording cycle, the density of a recorded image may be decreased. In order to eliminate this drawback, the thermal head is pre-heated in a thermal printer, facsimile machine or the like prior to a recording operation. Pre-heat prevents electrodes of heating resistors of the thermal head from being corroded by moisture in air or of recording paper or by ions in a thermal agent when a voltage is applied to the thermal head and the heating elements are not energized (e.g., during transmission in a facsimile machine). In the pre-heat operation, predetermined data output to the thermal head is constant. The temperature of the heating resistors of the head must be kept as high as possible, while not causing color development when thermal recording paper is used.
"All black" data are transferred to the thermal head during pre-heat, and strobe signals are intermittently output to drive the heating elements. In general, when black data are respectively supplied to adjacent dots, heat storage is increased and color development tends to occur. In addition, when the same heating resistor is continuously energized, heat storage is increased to tend to cause color development. For example, color development of the recording paper tends to occur even within a short period of energization time.
Generally, pre-heating is performed when a temperature value less than a predetermined value is sensed by a temperature sensor for detecting the temperature of a thermal head. In order to prevent color development of thermal paper serving as a recording medium during pre-heat, the number of strobe signals or the number of energization cycles is reduced, or the temperature value for starting pre-heat must be reduced. Since the temperature of the thermal head cannot be sufficiently increased during pre-heat, all of the benefits of pre-heat cannot be realized. In another thermal printer wherein its heating resistors are divided into N blocks and heating is performed in each unit of blocks, pre-heat time may tend to be prolonged.